Add local and loopback IPv6 addresses to url_preview_ip_range_blacklist

[thegcat]

I haven't tested wether the preview spider supports IPv6, but if it does (and probably even if it doesn't so there's no bad surprises when it does) the local and loopback and ULU/ULA and so on should be included in the example.

What comes to mind would be ::1/128, fe80::/64 and fc00::/7.

[richvdh]

there is no default blacklist. I presume you mean adding these to the example config?

PR welcome to do so. It should be trivial.

[thegcat]

This is what I meant indeed, I can see to provide one in the next few days.